JP6889026B2 - Power converter - Google Patents

Description

The present invention relates to a power converter

A power conversion device capable of detecting a voltage fluctuation of a system voltage and preventing an overcurrent is known. Patent Document 1 is an example of such a power conversion device.

Japanese Unexamined Patent Publication No. 2004-153957

Control responsiveness can be improved by selecting an LPF with a shorter time constant than usual for the detection value of the interconnection point voltage used for voltage feedforward of the inverter ACR when the system voltage fluctuates, but for all system accidents Further control responsiveness is required for higher demands such as continuing operation without stopping the gate. If a system fault point occurs on the primary side of the interconnection transformer, a delay in following the secondary voltage (output voltage of the power converter) will occur, so it is necessary to further improve responsiveness and suppress overcurrent as small as possible. is there.

It has an inverter connected to the system via an LC filter and an inverter control unit that controls the inverter. The control performed by the inverter control unit includes the inverter output current sampled multiple times within the calculation cycle and the inverter chain. Estimates the transient fluctuation current suppression voltage estimate, which is the voltage deviation at the time of a system accident, based on the interconnection point voltage of the system point, and feeds the transient fluctuation current suppression voltage estimate to the signal that controls the current flowing through the inverter. Provided is a power converter having a control in which a voltage command is created by adding as a forward and the voltage command is used as a voltage command for PWM of an inverter.

It is possible to provide a power conversion device that can respond to a sudden change in the system voltage at a high speed and suppress the generated overcurrent value to a small value.

The block diagram which shows the power conversion apparatus of this Example. The processing flow diagram of the voltage estimation calculation unit for suppressing transient fluctuation current. Interconnection point voltage fluctuation detection processing flow chart. FIG. 5 is a comparison diagram of the system voltage and output current when the system voltage of the conventional method and the system voltage of this embodiment suddenly changes.

Hereinafter, examples of the present invention will be described in detail with reference to the drawings. In the text, the symbol enclosed in [] indicates the vector quantity, the symbol not enclosed in [] indicates the scalar quantity, and in the figure, the vector quantity is indicated by adding an arrow above the symbol. In addition, || indicates the absolute value of the vector quantity enclosed by this.

FIG. 1 shows an outline of the power conversion device 2 of this embodiment. In this figure, the DC voltage generated by natural energy is used as the input 1, and the output 16 of the power conversion device 2 shown as within the outline of the alternate long and short dash line is connected to the system 18 via the interconnection transformer 17. The natural energy may be, for example, solar power generation, wind power generation, or the like.

The DC voltage input 1 using natural energy as an energy source is input to the input circuit 5 of the interconnection inverter 6. The AC output circuit 11 of the interconnection inverter 6 is connected to the secondary circuit 16 of the interconnection transformer 17 via an LC filter 14 for the purpose of reducing harmonics.

Next, the inverter control unit 21 will be described. The inverter control unit 21 that controls the interconnection inverter 6 includes an ACR3 that is a current controller. The ACR3 includes a DC voltage command _{V dc ref of the power converter 2 and a current command I ref} which is an output of the DC voltage controller DC- _{AVR 4} having a DC voltage detection value V dc as an input, and an interconnection point current detection value [ I] and the phase signal [V _2ph ] calculated by the phase detection unit 19 are input. The phase detection unit 19 takes the interconnection point voltage detection value [V ₂ ] as an input, and inputs the phase signal [V _{2ph ] of the interconnection point voltage [V 2} ] calculated by the phase detection unit 19 to the current regulator (ACR 3). The current regulator (ACR3) outputs and performs vector control that outputs _{[V 2ph} ] as an input and outputs an AC voltage command value [V _ref].

Next, the voltage feedforward [V _FF ] to be added to the AC voltage command [V _ref ] of ACR3 will be described. The voltage feedforward [V _FF ] is calculated from the interconnection point voltage detection value [V _2].

_{The low-pass filter passing value [V LPF} ] from which the harmonics are removed by the low-pass filter (LPF) 13 from the interconnection point voltage detection value [V ₂ ] is connected to the input terminal 9 of the switch 10. _{Further, the output signal [V est} ] of the voltage estimation calculation unit 12 for suppressing transient fluctuation current with the interconnection point voltage detection value [V ₂ ] and the interconnection point current detection value [I] as inputs is input to the input terminal 8 of the switch 10. Connect to. The voltage feedforward [V _FF ] uses the signal [V _LPF ] or [V _est ] selected by the switch 10. The above-mentioned inverter control unit 21 executes the calculation at 1/2 of the pulse period of the inverter. When the low-pass filter pass value [V _LPF ] is selected for voltage feedforward by switch 10. It is equivalent to the conventional inverter control.

Next, the voltage estimation calculation unit 12 for suppressing transient fluctuation current will be described. The voltage estimation calculation unit 12 for suppressing transient fluctuation current suppresses the interconnection point current [I] and the interconnection point voltage [V ₂ ] obtained by sampling N times (N ≧ 2) within the calculation cycle detected by the current sensor 15. _{Is the input, and the voltage change estimation value Δ [V 12} ] applied between the primary and secondary of the interconnection transformer 17 due to the current transient fluctuation is subtracted from the detection voltage [V ₂ ] to obtain the transient fluctuation current suppression voltage estimation value [V _est ]. It has a function of outputting to the terminal 8 of the switch 10. Here, the calculation cycle in this embodiment is a time corresponding to the calculation cycle of the output waveform control calculation of the PCS.

Here, the calculation method of the transient fluctuation current suppression voltage estimated value [V _est ] will be described using Equations 1 to 3, and the calculation processing flow will be described with reference to FIG.

_{Equations 1 to 3 are calculation formulas for obtaining the} voltage estimation value [V est] for suppressing transient fluctuation current, and the impedance of the interconnection transformer 17 due to the interconnection point voltage [V ₂ ] and the current transient fluctuation, and the point of failure. It is obtained from the difference from the estimated voltage change value Δ [V _{12] applied to the system impedance.}

The estimated voltage change value Δ [V ₁₂ ] is the voltage drop due to the interconnection trans-impedance generated when the power system on the primary side of the interconnection transformer 17 is momentarily lowered and the current flowing through the system impedance up to the accident point. It corresponds to the deviation voltage between the voltage and the secondary side voltage of the transformer (interconnection point voltage [V _{2] (inverter output voltage)).} Since AC overcurrent is generated due to this deviation voltage, the voltage change estimated value Δ [which is the deviation voltage from the _{interconnection point voltage [V 2} ] (inverter output voltage) as shown in Equation 1 to compensate for this. Except for V _{12 ], calculate the voltage estimate [V est} ] for suppressing transient fluctuation current and use it as the voltage feed forward [V _FF ]. The estimation calculation unit 12 operates at a cycle of 1 / N of the calculation cycle of the inverter control.

_{The estimated voltage change value Δ [V 12} ], which is the amount of voltage drop to the accident point when the system voltage suddenly changes, is calculated by Equation 2. The resistance R component and the inductance L component in Equation 2 correspond to R and L from the inverter to the infinite bus voltage. The line impedance [Z] = R + jωL from the voltage detection point of the inverter to the infinite bus voltage is the impedance of the interconnection transformer 17 ([Z _Tr ] = R _Tr + jωL _Tr ) and the primary side of the interconnection transformer 17. system impedance estimates from the terminal to the infinite bus equivalent to [Z _g] total impedance is the sum of _{(= R g + jωL g)} [Z] = R Tr + R g + jω (L Tr + L g) .. Since it is difficult to actually obtain the system impedance [Z _g ], the estimated value from the short-circuit capacitance is used. Here, since the R component is sufficiently smaller than the L component, it is ignored and the right side of Equation 2 is obtained. The differential term di / dt is obtained from the average value Δ [I _{ave ] of the temporal change Δ [I N-1} ] of the interconnection point current in the calculation period Ts and the sampling period Δt (= T _s / N). Here, Δ [I _ave ] is detected by the previous sampling for each sampling on the premise that the interconnection point current is _{sampled N times (N ≧ 2) within the calculation cycle T s, as shown in Equation 3.} By calculating the difference between the value and the value detected in this sampling, the amount of time change of the interconnection point current Δ [I _m-1 ] / (T _s / N) (= ([I _m ]-[I _m-1] ]) / (T _s / N)) is calculated and the sum is divided by N. By calculating the average value Δ [I _ave ] of the amount of time change of the interconnection point current, it is possible to suppress the influence on the momentary noise mixed in the interconnection point current detection value.

FIG. 2 is a flow chart of a voltage estimation calculation unit for suppressing transient fluctuation current. The time change amount of the interconnection point current with the interconnection point current [I _{1 ] of the first sampling and the interconnection point current [I 0} ] of the 0th sampling (the last value sampled within the previous calculation cycle) as inputs. Calculate Δ [I ₁ ] (= [I ₁ ]-[I ₀ ]) (process 1), then the interconnection point current [I ₂ ] for the second sampling and the interconnection point current [I 2] for the first sampling. _{With 1} ] as the input, the time change amount Δ [I ₂ ] (= [I ₂ ]-[I ₁ ]) of the interconnection point current is calculated (process 2). This is repeated until the Nth sampling (N ≧ 2), and each current change amount is obtained from Δ [I ₁ ] to Δ [ _IN ]. Using these current changes, the average value Δ [I _ave ] of the current changes is calculated (process N). Next, using the average value Δ [I _ave ] of the current change amount and the total impedance estimated value [Z], the voltage change estimated value Δ [V ₁₂ ] due to the interconnection transformer 17 and the system impedance when the system voltage drops is calculated. .. The estimated voltage for suppressing transient fluctuation current [V _est ] is calculated from the difference between this and the value of the interconnection point voltage [V ₂ ] (processing N + 2). The above is the calculation flow of the voltage estimation calculation unit for suppressing transient fluctuation current.

Next, the interconnection point voltage fluctuation detection unit 7 describes the command SWREF that selects the output of the switch 10. FIG. 3 shows the processing flow of the interconnection point voltage fluctuation detection unit 7. The fluctuation detection unit 7 takes the interconnection point voltage [V ₂ ] as an input and _{calculates the amplitude | [V 2} ] | of the interconnection point voltage (process 1). In this amplitude calculation, the UVW phase of the interconnection point voltage [V ₂ ] is αβ-converted using Equation 4, and the amplitude is calculated using Equation 5 from _{the voltages [V α} ] and [V _{β] after the αβ conversion.} To do. Command to select switch terminal 8 (process 3) when | [V ₂ ] | is smaller than the predetermined value | [V ₀ ] | (process 2), and select switch terminal 9 (process 4) when it is larger. The SWREF is output to the switch 10.

FIG. 4 is a simulation waveform of the system voltage and the output current when the system voltage of the power conversion device to which this embodiment is applied and the power conversion device using the conventional method suddenly changes. In both this embodiment and the conventional method, these waveforms are waveforms in which the system voltage suddenly changes from 100% to 0% at 0 seconds, and the output current of the conventional method jumps up to 150% at 0 seconds. In the conventional waveform of FIG. 4, the operation of the PCS is stopped when the current exceeds 150%, and when the PCS continues to operate, it rises to 6pu. On the other hand, in this embodiment, the output current is suppressed to jump up to about 140% at time 0 seconds, and the current value can be reduced.

When the system voltage fluctuates abruptly, the voltage feed forward [V _FF ] of the inverter current control ACR3 is switched from the low pass filter output [V _LPF ] to the transient fluctuation current suppression voltage estimate [V _{est] to [V est]. By using est} ], tracking to sudden changes in system voltage is speeded up, overcurrent can be prevented, and operation can be continued. Furthermore, by sampling the current a plurality of times _{and calculating Δ [I ave} ] based on the difference from the previous value, the influence of the detection noise of the interconnection point current can be suppressed. This is because, for example, when the interconnection point current changes at a constant rate, momentary noise is mixed in the interconnection point current at the time of the 0th sampling, and the difference between the 0th and 1st times becomes large. However, since the average value of the current change is calculated using the difference between the first and second times and the difference between the N-1th time and the Nth time after that, the influence of noise mixed in the current change detection value is reduced. It becomes possible to suppress it.

In this embodiment, an example is shown using an AC-based (phasor) equation, but the same effect can be obtained by using the detected value after conversion to a DC-based after DQ conversion.

1 Input of power converter 2 Power converter 3 Current controller (ACR)
4 DC voltage controller (DC-AVR)
5 Interconnected inverter input 6 Interconnected inverter 7 Interconnected point voltage fluctuation detector 8 [V _est ] Selection switch terminal 9 [V _LPF ] Selection switch terminal 10 Switch 11 Interconnected inverter output 12 Transient fluctuation current suppression voltage estimation Calculation unit 13 Low-pass filter 14 LC filter 15 Current sensor 16 Power conversion device output 17 Interconnection transformer 18 system 19 Phase detection unit 20 Power conversion device 21 Inverter control

Claims (4)

An inverter connected to the system via an LC filter,
It has an inverter control unit that controls the inverter, and has an inverter control unit.
The control performed by the inverter control unit includes
Transient fluctuation current suppression by removing the voltage change estimated value, which is the voltage deviation at the time of a system accident, from the interconnection point voltage based on the inverter output current sampled multiple times within the calculation cycle and the interconnection point voltage of the inverter interconnection point. Calculate the voltage estimate for
A voltage command is created by adding the transient fluctuation current suppression voltage estimate as feedforward to the signal that controls the current flowing through the inverter.
There is a control that uses the voltage command as a PWM voltage command for the inverter.
Power converter. The inverter control unit includes a switch capable of switching between two inputs according to the magnitude relationship between the inverter interconnection point voltage value and a predetermined value.
One input to the switch is the voltage estimation value for suppressing the transient fluctuation current, and the other input is the LPF passing value of the interconnection point voltage of the inverter interconnection point.
The power conversion device according to claim 1, wherein the output of the switch is used as a voltage feedforward to be added to the output of the inverter current control. The power conversion device according to claim 2, wherein the inverter control unit uses the estimated voltage for suppressing transient fluctuation current as a voltage feedforward when the inverter interconnection point voltage value is smaller than a predetermined value. The power conversion device according to claim 1, wherein the calculation cycle is a value halved of the cycle determined by the carrier frequency of the inverter.

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